Unlike conventional resources based on petrochemical industry, 1,4:3,6-dianhydrohexitol is a bio-based material derived from a biomass, i.e., a renewable resource containing polysaccharide as its components such as corn, wheat, sugar, and the like. Particularly, in case of a bioplastic containing a bio-based material, carbon dioxide (CO2) produced during waste disposal processes after the use of a bioplastic can be reused for the growth of biomass, and thus the bioplastic has been noticed as a carbon dioxide reduction material to prevent global warming, which is a serious worldwide issue.
1,4:3,6-Dianhydrohexitol exists in three different forms of stereoisomers, which has different chemical properties depending on the difference in the relative configuration of two hydroxyl groups present therein: isomannide (as shown in formula a below, mp: 81-85° C.), isosorbide (as shown in formula b below, mp: 61-62° C.), and isoidide (as shown in formula c below, mp: 64° C.). Particularly, in a case where 1,4:3,6-dianhydrohexitol is used as a monomer material of polycarbonate which is one of representative engineering plastics, the polycarbonate thus prepared can have good thermal and optical properties owing to molecular structural characteristics of 1,4:3,6-dianhydrohexitol, i.e., rigidity and saturated heterocyclic structure, together with the advantages of a bioplastic.

Since 1,4-dimethyl-cyclohexane dicarboxylate (hereinafter referred to as DMCD) or 1,4-cyclohexanedicarboxylic acid (hereinafter referred to as CHDA), a hydrolysis product of DMCD, has a cyclohexane ring structure in the center of the molecule. Thus, if these materials are introduced into a polymer chain, they improve the weatherability and UV stability of the polymer, and also allow the polymer to have excellent material properties, such as gloss retention, yellowing resistance, hydrolytic stability, corrosion resistance, and chemical resistance, owing to its unique combination of flexibility and hardness in the molecular structure.
Poly(1,4-cyclohexylidene 1,4-cyclohexanedicarboxylate) (hereinafter referred to as PCCD), a DMCD/CHDM homopolyester, is an example of commercially available polymer materials developed by using DMCD. Owing to its superior properties such as weatherability, chemical resistance, flowability, and a low refractive index, PCCD has been used to develop a polycarbonate/PCCD alloy (product name: Xyrex) by DuPont (USA) in order to improve transparency of polycarbonate.
A commercial manufacturing process of polycarbonate can be divided into two processes: solution polymerization and melt polycondensation. Unlike the solution polymerization process where phosgene is used as a source material for carbonate, diphenyl carbonate (hereinafter referred to as DPC) is used in the melt polycondensation process. Thus, raw materials used in the conventional melt polycondensation process generally include DPC and bisphenol A (hereinafter referred to as BPA), which is a diol; and a transesterification reaction of BPA with DPC produces phenol as a byproduct of the melt polycondensation.
Meanwhile, it is required to convert a functional group present in DMCD or CHDA into another functional group, which may cause the production of phenol as a byproduct via a transesterification reaction with diol, in order to use DMCD or CHDA in the polycarbonate melt polycondensation. For example, dimethyl ester of DMCD or dicarboxylic acid of CHDA needs to be converted into diphenyl ester. Thus, an example of diphenyl ester derivatives of DMCD or CHDA which can be used for the polycarbonate melt polycondensation is 1,4-diphenyl-cyclohexanedicarboxylate (hereinafter referred to as DPCD), and is synthesized by a reaction of DMCD or CHDA with phenol, as represented by Reaction Scheme 1 below:

In general, in case of 1,4-dimethyl-terephthalate (a tertiary dimethyl ester) and terephthalic acid (a diacid), a reaction does not occur therebetween if either one of their functional groups, i.e., one of acid and alcohol, is not activated. In case of DMCD (a secondary dimethyl ester) and CHDA (a diacid), however, they can react with phenol in a molten state, and thus it is easier to conduct DPCD synthesis.
The present invention employs DPCD, which is used as a material for forming an ester bond in the polymer chain, to provide an isosorbide-based polycarbonate ester (or polyester carbonate). The polycarbonate ester thus obtained is a novel bioplastic having high heat resistance and transparency whose properties and forming processability can be adjusted according to its needs by varying the DPCD content. The bio-based polycarbonate ester according to the present invention can exhibit the same level of heat resistance as compared to the conventional bioplastic disclosed in US 2011/0003101 A1, even comprising a less amount of isosorbide, and thus have a relative advantage in terms of production costs.